In recent years there has been a rapid growth in the reported use of automated image processing systems to analyse images obtained from video and digital cameras mounted on optical microscopes. However, the benefits of using such systems have been offset by the need to manually load and unload microscope slides on the microscope.
There is no stand-alone automated slide loader in the market that loads and unloads slides to and from an external, free-standing optical microscope. Current processes of loading and unloading slides are either performed manually or require a dedicated instrument that already has a built-in microscope and imaging system.
There are several patents that describe systems to automatically load and unload slides onto microscopes including U.S. Pat. No. 4,248,498 (Georges), and U.S. Pat. No. 4,501,495 (Faulkner). These patents describe systems whereby the slide loader is integrated into a microscope/imaging platform. It is not possible with these designs to interface to free-standing microscopes.
Slide holders on current model microscopes typically consist of a spring loaded pivot arm to position and clamp slides onto the slide holder. One form of slide holder disclosed is U.S. Pat. 4,159,875 (Hauser). The shortcomings of such holders include:
a) they are limited to manual operation only. They require the user to manually open the clamping mechanism, accurately position the slide on the slide holder, and then release the clamping mechanism. Consequently, such methods are not suited to automated scanning systems as they require constant attendance from laboratory staff to load and unload slides.
b) the positional accuracy achieved by manually locating slides is not always guaranteed.
The use of vacuum chucks as an alternative means to clamp slides on microscope stages have been described in U.S. Pat. No. 4,508,435 (Graham) and U.S. Pat. No. 4,981,345 (Berry). These chucks can accommodate X and Y motion of the stage by the use of flexible vacuum connections but have the following shortcomings:
a) positional accuracy of the slide under the microscope is not guaranteed either by manual or robotic positioning;
b) considerable modifications to a microscope stage are required to accommodate vacuum lines (a vacuum pump is also required but can be mounted away from the microscope).
c) to obtain adequate clamping (suction) of a slide, both ends of the slide would require vacuum thereby reducing the effective scan area on the slides. Therefore critical features on the slide may be missed.
d) Vacuum chucks and associated plumbing can obstruct the optical path between a microscope's condenser and objective lens.
U.S. Pat. No. 4,012,111 describes a slide holder that requires the user to position the slide by hand and push to clamp the slide down. It claims to be able to position slides accurately and repeatedly. The shortcomings of this holder are:
a) the slide holder can only be used manually as it request the user to manually place the slide against one slide retainer before the slide could be clamped down.
b) the slide holder requires a user to use two hands to position a slide correctly; one hand to hold the slide against the fixed locaters on the back and the slide retainer, and the other hand to clamp the slide. It is not designed to automatically locate the slide.
c) the positional accuracy in the x-y plane is dependent on human placement of the slide.
d) the positive force required to clamp the slide into position may lead to crack and chipping of slides.